The present invention relates to a vehicle occupant protection system for protecting the vehicle occupant from the impact of a vehicle crash, and in particular to a vehicle occupant protection system which can favorably control the time history of the deceleration acting on the vehicle occupant at the time of a vehicle crash so as to minimize the injury to the vehicle occupant.
When a vehicle frontally crashes onto a rigid body, because the seat belt inevitably has a certain slack and has a property to elongated under a tension, even though the vehicle occupant is restrained by the seat belt to a certain extent, the vehicle occupant continues to move forward under the inertia force. The forward movement of the vehicle occupant extends the seat belt, and the deceleration of the vehicle occupant peaks when the maximum extension of the seat belt has occurred. The peak of the deceleration of the vehicle occupant is normally greater than the peak of the deceleration of the vehicle body.
Normally, the extent of the injury to the vehicle occupant at the time of a vehicle crash is dictated by the maximum level of the deceleration of the vehicle occupant, and it is therefore desirable to reduce the maximum level of the deceleration of the vehicle occupant to as low a value as possible.
To minimize the deceleration of the vehicle occupant, it is necessary not only to reduce the average deceleration of the vehicle but also to control the deceleration pattern so as to reduce the elongation of the seat belt. To achieve this goal, it has been proposed to follow a pattern of deceleration in which a deceleration level higher than the average deceleration is produced in the vehicle seat in an early stage of the vehicle crash, and a deceleration in an opposite direction is produced in the vehicle seat for a short time period before the vehicle occupant is finally decelerated at the final steady deceleration of the vehicle body. For details of such earlier proposals, reference should be made to copending patent applications Ser. Nos. 09/648,190 filed Aug. 23, 2000, 09/608,669 filed Jun. 30, 2000, 09/377,366 filed Aug. 19, 1999, and 09/376,888 filed Aug. 18, 1999. The contents of these applications are hereby incorporated in this application by reference.
According to a conventional vehicle body structure (for instance, see Japanese patent laid open publication No. 07-101354), a crash reaction force generating member such as side beams and a crushable zone defined by the gaps between various components are placed in a front part of the vehicle body, and the deceleration pattern of the passenger compartment is controlled by absorbing the energy of the crash with the deformation of such parts. However, according to this prior proposal, it may be possible to control the deceleration level of the passenger compartment to a constant level (square wave), but a more effective deceleration pattern cannot be achieved.
In view of such problems of the prior art and the recognition by the inventors, a primary object of the present invention is to provide a vehicle occupant protection system which can achieve a favorable deceleration pattern for the seat belt and thereby effectively reduce the maximum deceleration of the vehicle occupant.
A second object of the present invention is to provide a vehicle occupant protection system which is suitable for use in small cars where the permitted forward movement of the vehicle occupant at the time of a vehicle crash is relatively limited.
A third object of the present invention is to provide a vehicle occupant protection system which can minimize the injury to the vehicle occupant at the time of a vehicle crash under all conditions.
According to the present invention, these objects can be accomplished by providing a vehicle occupant protection system, comprising: a seat for seating a vehicle occupant in a passenger compartment of a vehicle body; a seat belt provided in association with the seat for restraining a vehicle occupant seated in the seat; a power actuator interposed between an end of the seat belt and a fixed part of the vehicle body and adapted to pull the seat belt in a direction to increase a restraint on the vehicle occupant; and a sensor for providing an activation signal to the power actuator upon detection of a vehicle crash; wherein the power actuator is adapted, when a vehicle crash is detected, to apply a rearward acceleration to the seat belt end in an early phase of the vehicle crash according to a prescribed pattern. Typically, the prescribed pattern includes an initial crash stage for moving the seat belt rearward at a deceleration which is earlier and greater than a deceleration produced in the vehicle body, and an intermediate crash stage for controlling the rearward movement of the seat belt so as to substantially equalize the deceleration acting on the vehicle occupant with the deceleration acting on the vehicle body.
When a vehicle crashes frontally onto an object, the front part readily deforms as it consists of relatively soft members, and then more rigid structural members start deforming. On the other hand, it is desirable for the passenger compartment not to deform to any substantial extent to protect the vehicle occupant from secondary impacts. The time history of a vehicle crash therefore includes an initial gradual rise in deceleration accounted for by the deformation of the readily deformable part, and a steady deceleration which is accounted for by the deformation of the more rigid structural members. Also, the seat belt has a certain slack and a property to elongate when a tension is applied thereto. Therefore, upon occurrence of a vehicle crash, the deceleration of the vehicle occupant starts after a certain time delay caused by the deformation of the readily deformable part of the vehicle body and the slack/elongation of the seat belt, and then rises sharply when the deformation stroke of the readily deformable part of the vehicle body is exhausted and the slack/elongation of the seat belt has been exhausted. This sharp rise in deceleration which may be considered as a secondary impact which the seat belt applies to the vehicle occupant typically exceeds the steady deceleration of the vehicle body (passenger compartment). Because the extent of the injury to the vehicle occupant is dictated by the maximum level of the deceleration of the vehicle occupant, it is desirable to reduce the maximum level of the deceleration of the vehicle occupant.
According to the present invention, the seat belt applies a sharply rising deceleration in an early phase of a vehicle crash, typically before a part of the vehicle body supporting the seat has reached a steady deceleration level or before a part of the vehicle body supporting the seat has started decelerating as a result of the vehicle crash, so that the subsequent sharp rise in the deceleration of the vehicle occupant beyond a tolerable limit can be controlled.
According to a preferred embodiment of the present invention, the seat belt is provided with a second end which is engaged by the seat, the system further comprising a seat rail for permitting a fore-and-aft movement of the seat, and a second power actuator for moving the seat rearward, the second power actuator being adapted to apply a rearward acceleration to the vehicle seat in an early phase of the vehicle crash according to a prescribed pattern. This arrangement allows the seat belt to be pulled at at least two ends, and this contributes to a rapid rise in the level of deceleration which the seat belt applies to the vehicle occupant. In this case, the sensor may be adapted to activate only one of the first and second power actuators when an intensity of the vehicle crash is below a certain level, and activate both of the first and second power actuators only when an intensity of the vehicle crash is above a certain level.
A rapid rise in the level of deceleration which the seat belt applies to the vehicle occupant can also be achieved if the power actuator is interposed between the seat belt end which may consist of a shoulder anchor and the fixed part of the vehicle body via a mechanism for enlarging a displacement of the power actuator.